A touch panel refers to an input device for detecting a touch on a panel and providing a computer with a necessary command. There are various types such as a resistive film type, a capacitive type, a ultrasonic surface acoustic wave type, and an electromagnetic induction type, and the resistive film type and the capacitive type (to be accurate, a projected capacitive type) are in the main stream today, because there is not much difference in price between these types and these types can support multi-touch (detect a plurality of touch points).
In the resistive film type, a touch is detected with the same principle as that of a mechanical switch. That is, by using a force applied onto a panel, electrodes in the panel are turned ON. Therefore, a “pressing force” to some extent is required, although it is small. On the other hand, in the capacitive type, a touch is detected from a change in capacitance in the panel. This is because the human body can be regarded as a capacitor with a capacitance on the order of 100 pF and the capacitance is changed only with part of the human body (normally a fingertip; hereinafter typified by a fingertip) brought into contact with the panel. As such, while a necessary “pressing force” is required in the resistive film type, the capacitive type is different in that such a pressing force is not required. Therefore, since a touch panel of the capacitive type has an advantage of allowing a touch operation only with a fingertip brought into light contact with the panel, such a touch panel is expected to be developed in the future as being in the main stream as a touch panel for a portable phone, a portable information terminal, for example.
Meanwhile, the touch panel of the capacitive type can detect not only the touch operation described above (with a fingertip brought into light contact with the panel) but also a fingertip approaching operation (a so-called hover operation), because the capacitance of the panel is changed only with a fingertip brought near the panel. A hover operation can be detected by, for example, changing the sensitivity of the touch panel, but an erroneous detection may not be prevented only by simply enhancing the sensitivity. Moreover, there is an inconvenience of not being capable of differentiating between a touch operation and a hover operation.
<Patent Document 1 (Hereinafter, a First Conventional Technology>
This first conventional technology discloses a technology of differentiating between a touch operation and a hover operation according to the magnitude of a change in capacitance. However, this technology does not have an adjusting function for differentiating between a touch detection and a hover detection. Therefore, it is impossible to accurately and sufficiently differentiate among respective detections.
<Patent Document 2 (Hereinafter, a Second Conventional Technology>
This second conventional technology discloses a technology of differentiating between a touch operation and a hover operation based on a difference in signal pattern on a panel surface, specifically, a difference in pattern such that the surface of the fingertip in a non-contact state assumes a naturally rounded shape and therefore its signal pattern has a small area while the surface of the fingertip in a contact state is slightly crushed and a flat surface is spread and therefore its signal pattern is a bit large. However, while this technology can be said as having an adjusting function for differentiating between a touch detection and a hover detection (a method of examining the center of mass or others), its adjustment include estimation and the accuracy of differentiating between touch detection and hover detection is not sufficient.
<Patent Document 3 (Hereinafter, a Third Conventional Technology>
This third conventional technology describes a technology of changing detection resolution and detection sensitivity in a stepwise manner as an object (a fingertip) and the panel surface come closer to each other and sequentially scanning and detecting a distant hover operation, a near hover operation, and a touch operation for each step. That is, as depicted in FIG. 3 of this document, a minimum detection resolution and a maximum degree of detection sensitivity are applied to scan and detect a distant hover operation in a detection space I with distances Lp to Lq (where Lp>Lq) from the panel surface; an intermediate detection resolution and an intermediate degree of detection sensitivity are applied to scan and detect a near hover operation in a detection space II with next distances 0 to Lq; and a maximum detection resolution and a minimum degree of detection sensitivity are applied to scan and detect a touch operation at a final distance 0 (that is on the panel surface).